Mobile robots, including autonomously-navigating mobile robots, inertially-guided robots, remote-controlled mobile robots, and robots guided by laser targeting, vision systems, roadmaps and beacons, to name a few examples, normally use horizontally-oriented laser sensors to scan the area in the mobile robot's direction of travel and to detect potential obstacles in the mobile robot's path. The horizontally-oriented lasers, which typically scan in two-dimensional planes roughly parallel with floor, work reasonably well for detecting objects that extend from the floor in a substantially perpendicular direction, so long as the obstacle intersects the horizontally-oriented scanning plane. However, they do not work well for detecting positive physical obstacles in the mobile robot's path that are parallel to the floor and/or obstacles that are not at the same height as the horizontally-oriented scanning plane. This means the mobile robots frequently have no way of detecting and avoiding positive obstacles, such as long tables with legs at the ends (and no legs in the middle), objects suspended from a ceiling or other structure, and obstacles that stick out from the edge of another object, like a keyboard tray. Mobile robots that use horizontally-oriented lasers for detecting obstacles also have problems detecting and avoiding unexpected negative obstacles, such as a hole in the floor, a descending flight of stairs, the end of a loading dock or the edge of a cliff.
Previous attempts to solve these problems have included, for example, attaching a plurality of vertically-oriented or randomly-oriented lasers to the mobile robots and using the vertical or randomly-oriented lasers to detect obstacles parallel to the floor, as well as holes or drop-offs in the floor. However, there have been a number of significant disadvantages associated with such solutions, including prohibitively-high cost associated with installing, using and maintaining a multiplicity of expensive lasers, and an unacceptably high number of false positives arising, for example, from gratings in the floor, which do not necessarily need to be avoided by the mobile robot.